Truss connector plates are widely used for joining together wood members used in forming trusses, joists, beams and the like construction elements. Typically, such plates are made of thin, relatively stiff, sheet metal, such as galvanized steel or the like, with struck-out teeth that embed into the wood members. Examples of such plates are shown in U.S. Pat. Nos. 3,651,612 issued Mar. 28, 1972 and 4,207,719 issued June 17, 1980.
In use, wood members, as for example 2.times.4 strips are arranged on a flat surface, with their ends or other parts located in close proximity to provide a joint. A truss connector plate is placed over the joint location. By means of a suitable compression device, such as a hydraulic clamp, or by hammering, the plate is pressed against the wood so that its teeth embed into the wood to form a joint. The joints may be in different shapes and styles. For example, there may be two wood strips arranged side by side and simply joined together to form a double thick wood strip. Alternatively, the ends of wood strips may be joined together to form a double length. For truss constructions, the end of one strip may be angled and placed against a mid point of another strip and these may be joined together to form a truss. Numerous configurations are used. Typically, a pair of plates are used, one on each side of the wood member joint.
In the joint construction resulting from the use of typical connector plates, because the wood and its fibers are relatively flexible, over a period of time, there is a tendency for the teeth to loosen within the wood. This may be due to the effects of temperature and weather upon the wood fibers and also due to the movement of the wood members under varying loads. Regardless of the cause, there is a tendency for the teeth of the connector plates to move relative to the wood so that they loosen in gripping the wood.
In addition, the connector plates are designed to handle predetermined shear loads. Thus, more plates or larger size plates or increased thickness plates must be used for increased anticipated shear loads.
Thus, there has been a need for plates which tend to more tightly grip and resist dislodgment from the wood and also, to increase the load handling capacity of each plate, particularly the shear loads, without substantially increasing the costs of the plates.